1. Field
Embodiments relate to a light source module and a planar light source device.
2. Description of the Related Art
A representative example of light-emitting elements is Light-Emitting Diodes (LEDs), which convert electrical signals into infrared light, visible light, and the like using the characteristics of compound semiconductors. LEDs are used in, for example, home appliances, remote controllers, electronic display boards, display devices, and various automated devices. The fields in which LEDs are used are gradually becoming more numerous.
A planar light source device equipped with LEDs is a device that converts light, which is emitted from LEDs in a point light source form, into a planar light form. The planar light source device may be used in a display apparatus such as a liquid crystal display apparatus, and may be used in a variety of other lighting apparatuses.
In a conventional light guide structure, light is introduced from a light source, located at one side when viewing a cross-section of a light guide unit, into the light guide unit so as to be guided to a light emission surface or a surface opposite the light source. A light guiding means is a total reflection or light emission means based on the difference in the index of refraction, and such a means uses a pattern or shape to cause light to be emitted from the light emission surface.
FIG. 9 is a cross-sectional view of a conventional planar light source device, taken along the longitudinal direction of a light source module. Referring to FIG. 9, the conventional light source module is constructed such that packages 1300 are disposed so as to surround point light sources 1200. The packaged point light sources 1200 are arranged at a constant pitch in the longitudinal direction of a circuit board 1100.
In order to concentrate light generated from the point light sources 1200 in a desired direction, the packages 1300 are configured so as to be open at upper sides thereof over the point light sources 120 and to surround the side surfaces of the point light sources 1200.
Although the packages 1300 may concentrate light, generated from the point light sources 1200, upward (toward a light guide plate 1400), there is a problem in that the amount of light emitted in a lateral direction is reduced, thereby causing the occurrence of hot spots between the point light sources 120.
For this reason, if the pitch between the point light sources 1200 is decreased in order to diminish the hot spots, there is a problem in that manufacturing costs are increased.
FIG. 10 illustrates the travelling path of light introduced from a light source module in which the light is guided toward a light guide plate 1400 by means of a light guide 1500.
Here, the light guide 1500 is configured such that the width thereof is reduced with increasing distance toward the light guide plate 1400 from the point light sources 1200.
Consequently, there is a problem in that the light introduced from the point light sources 1200 undergoes total reflection in the light guide 1500, thereby causing internal loss of light. Furthermore, when light emitted from the light guide 1500 is introduced into the light guide plate 1400, some of the light introduced at an angle exceeding an acceptance angle (the maximum allowable incident angle within which the light emitted from the light guide plate 1400 can undergo total reflection), thereby causing radiation loss in the light guide plate 1400.
The formula for calculating the acceptance angle is as followsin α=√{square root over (n12−n22)}wherein α is an acceptance angle, n1 is an index of refraction of a light guide plate, and n2 is an index of refraction of the outside of the light guide plate.